The present invention relates to a process in joining, more precisely a process in roll folding, where a folding roller is moved, with resilient compressive force, against a workpiece in a path along it by means of a movement device provided with a control system.
In the joining together of two sheet metal parts in such contexts where the demands on surface finish are high, folding or roller folding is often employed as a superior alternative to welding. Roller folding proceeds such that one of the workpieces is given an edge portion projecting out over the other workpiece, the edge portion being folded in over the other workpiece and urged against it so that the edge of the other workpiece will be accommodated between the first workpiece and its folded-over edge portion. During this working cycle, the workpieces rest on and are positionally fixed in relation to a bed which thereby will define the form of the finished fold.
For the above-mentioned folding over of the edge portion of the first workpiece, use is made of a roller which is displaced in the longitudinal direction of the edge portion. Before the folding operation, the first workpiece has its edge portion projecting approximately at right angles or at least transversely directed in relation to the plane of the portion of the workpiece lying inside the edge portion. The roller is then generally moved in three different steps along the edge portion so that this, in a first folding step, is bent at approximately 30xc2x0 and in a second folding step an additional approximately 30xc2x0. The subsequent and last folding step is the crucial step when the surface finish of the workpiece is determined.
The two first folding steps may be carried out without any major requirements on precision in the relative positions between the folding roller and the edge portion of the workpiece. This also applies to the compression force which prevails between the folding roller and the edge portion.
On the other hand, as regards the final step in the folding operation, extremely high demands on the precision of movement are placed, as well as demands on a certain resilience capability in the roller. In addition, the compression force from the roller on the edge portion resting on the bed must often vary along the length of the edge portion so that, for example, in a tightly bent xe2x80x9ccorner regionxe2x80x9d of the workpiece, the compression force must be reduced since the edge portion must be considerably narrower in such a curved region.
EP 577 876 shows, with reference to FIGS. 7 and 8; and 9 and 10, respectively, apparatuses for roller folding. Common to both of these embodiments is that an industrial robot carries an end effector or folding head with two main components, where the one main component is connected to the industrial robot while the other main component is movable in relation to the first towards and away from the workpiece, The construction includes a servo apparatus by means of which the mutual position of the two main components can be controlled in order thereby to vary or realise a resilient force in the abutment of the folding roller against the workpiece.
The described embodiments may be feared to suffer from serious drawbacks as regards the precision in the abutment force of the folding roller and its path of movement because of the movable interconnection of the main components in the folding head. Further, the folding head will, naturally, be extremely complicated and expensive.
Further drawbacks in the prior art technology reside in the fact that the apparatus in principle comprises two different movement mechanisms, one for displacing the folding head and one for displacing the folding roller in the folding head. This implies that there are two sources of defective precision both as regards the compression force and accuracy in the path of movement of the roller.
The present invention has for its object to formulate the process intimated by way of introduction such that the drawbacks inherent in prior art methods and apparatuses are obviated. In particular, the present invention has for its object to realise a process which may be reduced into practice without the employment of complicated and expensive specialist equipment. Further, the present invention has for its object to realise a process which affords precision advantages compared with prior art technology.
The object forming the basis of the present invention will be attained if the process intimated by way of introduction is characterised in that the resilience is generated by means of the movement device.
As a result of this feature, advantages will above all be afforded as regards simplicity in the equipment.